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Nelson, L.A., Voss, R.D. and Pesek, J.T. (1985) Agronomic and statistical evaluation of fertilizer response. In: Engelstad, O.P., Ed., Fertilizer Technology and Use, ASA, Madison, 53-90.

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• TITLE: Sources of inaccuracy when estimating economically optimum N fertilizer rates

  AUTHORS: Martin Bachmaier

  KEYWORDS: Confidence Interval; Economic Optimum; N Rate Trials; Quadratic Model; Linear-plus-Plateau Model

  JOURNAL NAME: Agricultural Sciences, Vol.3 No.3, May 15, 2012

  ABSTRACT: Nitrogen rate trials are often performed to determine the economically optimum N application rate. For this purpose, the yield is modeled as a function of the N application. The regression analysis provides an estimate of the modeled function and thus also an estimate of the economic optimum, Nopt. Obtaining the accuracy of such estimates by confidence intervals for Nopt is subject to the model assumptions. The dependence of these assumptions is a further source of inaccuracy. The Nopt estimate also strongly depends on the N level design, i.e., the area on which the model is fitted. A small area around the supposed Nopt diminishes the dependence of the model assumptions, but prolongs the confidence interval. The investigations of the impact of the mentioned sources on the inaccuracy of the Nopt estimate rely on N rate trials on the experimental field Sieblerfeld (Bavaria). The models applied are the quadratic and the linear-plus-plateau yield regression model.